HeXH shared with us her relative centroid location code, an example, and several related documents in 2019/08/01 in Yunnan. The method has been developed in several recent publications.
Several main steps in the code include: 1. relative location of main and reference event; 2. CAP for main and relative event; 3. caluclate the backazimuthal vairation and determine the rupture direction.
The code manly includes three corresponding parts, which is documented in the readme file in detail.
Step1:
The relative relocation code include the getsolv.sh, get3.awk, and solv3.awk, of which the getsolv.sh is the main code. The main equations used in the code seem to be, $\left( \begin{matrix} 1 & \cos{\theta} & \sin{\theta} \\ \cos{\theta} & \cos^2{\theta} & \cos{\theta} \sin{\theta} \\ \sin{\theta} & \cos{\theta} \sin{\theta}& \sin^2{\theta} \end{matrix} \right) \left( \begin{matrix} \Delta T_{err} \\ \Delta X_{Lon} \\ \Delta X_{Lat} \end{matrix} \right) = \alpha \left( \begin{matrix} \Delta t \\ \Delta t \cos{\theta} \\ \Delta t \sin{\theta} \end{matrix} \right)$
Where $\theta$ is the azimuth angle of the main shock.
Step2:
Use the cut-and-paste method (CAP) to determine the focal mechanism and time shift for each station for both the main shock and reference event.
The scripts include step1_rot_chdelta.sh, step2_fk.sh, and step3_cap.sh.
The file obtain in step1(newloc) is used by geneNewDist.sh to rewrite the header of the sac file
Step3:
Least square to obtain the directivity, including do_directivity.sh and do_directivity_grid.sh. fit.f95 and fit_search.f95 are used here.